Rebuilding head will cost maybe three times your quote, unless you have a friend that can do all that work. Swapping the heads would be the way to go but either case you need to have it checked out. Not sure about horse power difference, but basically same motor, cam, compression, head work and bigger intake valves (powereglide cars) plus carburation etc etc can make power. For me the major factor is rear end gears, 47 had swapped in a 54 passenger 3:55 diff from a powerglide car, that made her love the freeway.
